Trastuzumab resistance, which is a common therapeutic challenge in HER2 positive metastatic breast cancer, is not fully understood. Pyrotinib is an oral tyrosine kinase inhibitor targeting EGFR, HER-2 and HER-4 receptors. More general inhibition of ErbB family with pyrotinib could provide additional benefit. Inetetamab could bind to HER2 extracellular domain (ECD) with high affinity and inhibit proliferation of multiple HER2-overexpressing cancer cell lines as a single agent or in combination with trastuzumab. This study is designed to evaluate the efficacy and safety of pyrotinib and vinorelbine tartrate capsulesin with or without Inetetamab for first line treatment in patients with HER2 positive metastatic breast cancer who had early failure on or after trastuzumab treatment.

Inclusion Criteria:

Histologically or cytologically confirmed invasive breast cancer HER2 status must be prospectively, centrally tested and be HER2-positive based on central laboratory assay results Prior treatment for breast cancer in the adjuvant, unresectable, locally advanced, or metastatic setting must include both a taxane, alone or in combination with another agent, and trastuzumab, alone or in combination with another agent. Patients who have previously used pertuzumab will be allowed.

Documented progression (which occur during or after most recent treatment or within 6 months after completing of adjuvant therapy) of incurable, unresectable, locally advanced or metastatic breast cancer, defined by the investigator Measurable and/or nonmeasurable disease; participants with central nervous system-only disease are excluded Cardiac ejection fraction greater than or equal to (>/=) 50 percent (%) by either echocardiogram or multi-gated acquisition scan Eastern Cooperative Oncology Group (ECOG) performance status of 0 or 1

Exclusion Criteria:

History of treatment with pyrotinib Prior treatment with lapatinib or neratinib History of other malignancy within the last 5 years, except for appropriately treated carcinoma in situ of the cervix, non-melanoma skin carcinoma History of receiving any anti-cancer drug/biologic or investigational treatment within 28 days prior to randomization except hormone therapy Recovery of treatment-related toxicity consistent with other eligibility criteria History of radiation therapy within 28 days of randomization Brain metastases that are untreated, symptomatic, or require therapy to control symptoms, as well as any history of radiation, surgery, or other therapy, including steroids, to control symptoms from brain metastases within 2 months (60 days) of randomization History of symptomatic congestive heart failure or serious cardiac arrhythmia requiring treatment History of myocardial infarction or unstable angina Current severe, uncontrolled systemic disease (for example, clinically significant cardiovascular, pulmonary, or metabolic disease) Pregnancy or lactation Current known active infection with human immunodeficiency virus (HIV) or hepatitis C virus Presence of conditions that could affect gastrointestinal absorption: Malabsorption syndrome, resection of the small bowel or stomach, and ulcerative colitis